The below template code from one of the tutorials on the official SilverStripe website ("How to create a navigation menu") includes the template variable $Menu(1)
What does the (1) mean? What happens if it gets changed to something else?
<ul>
<% loop $Menu(1) %>
<li>
<a href="$Link" title="Go to the $Title page" class="$LinkingMode">
$MenuTitle
</a>
...
</ul>